1. Field of the Invention
The present invention relates to a process for making 3-(2-substituted acryloyloxy)-2-hydroxypropyltrialkyl ammonium chloride and its isomer, 2-(2-substituted acryloyloxy)-3-hydroxypropyltrialkylammonium chloride, wherein the substituent is hydrogen or lower alkyl of 1 to 4 carbon atoms.
2. Description of the Prior Art
The quaternary salt 3-methacryloyloxy-2-hydroxypropyltrimethylammonium chloride and its isomer 2-methacryloyloxy-3-hydroxypropyltrimethylammonium chloride are generally referred to as MAHTAC.
MAHTAC is a cationic vinyl monomer which can be polymerized or copolymerized with a number of other vinyl monomers to produce polymers which are useful in antistatic, flocculation or sludge dewatering applications. If high molecular weight polymers are to be synthesized without gellation due to crosslinking, it is essential that the MAHTAC purity with regards to molecules with two or more vinyl groups be very high. It is also essential that the yield be high for economic viability.
A significant number of references detailing the synthesis of MAHTAC have appeared over the last 25 years. However, it appears that only limited production of this material has occurred and that it is not presently being manufactured commercially. It is likely that this production has not occurred because of low yields and/or low purity associated with the prior art.
U.S. Pat. Nos. 3,321,649; 3,329,706; and 3,428,617 teach that MAHTAC may be prepared by reacting methacrylic acid with an aqueous solution of glycidyltrimethylammonium chloride (GTAC). The reactions are carried out in a homogeneous aqueous solution. The product must be precipitated, extracted or recrystallized before it can be used to make useful polymers. This method also produces the hydrolysis product of GTAC which is present in the mixture as a methacrylate salt: EQU CH.sub.2 .dbd.C(CH.sub.3)COO--+(CH.sub.3).sub.3 NCH.sub.2 CH(OH)CH.sub.2 (OH)
Separation of this salt from the desired product is difficult but if it is not removed, polymers made from the MAHTAC will be amphoteric and have reduced effectiveness due to intramolecular charge neutralization. U.S. Pat. No. 3,329,706 describes a process which produces purified MAHTAC in only 93% yield with a melting point of 176.degree.-178.degree. C. We have confirmed their Example 1 and produced MAHTAC with 70% yield and a melting point of only 176.degree.-178.degree. C.
Japanese Kokai 73/34,116 and 77/73,817 teach the synthesis of MAHTAC by reacting glycidylmethacrylate with trimethylamine hydrochloride. The synthesis is carried out in solvents such as alcohols, dimethylsulfoxide or sulfolane. Reaction products are separated by crystallization through cooling or the addition of a solvent such as acetone or cyclohexane. The references report yields of 78% or less and a melting point range of 180.degree.-182.degree. C. Japanese 73/34,116 also describes a method of reacting methacrylic acid and epihalohydrin to form a product which is then reacted with trimethylamine. They report that the reaction is very slow, polymerization losses can not be avoided and trimethylamine escapes from the reaction system. This reference teaches away from the use of the method.
U.S. Pat. No. 3,397,227 and British Patent 1,140,520 teach that MAHTAC may be prepared by treating methacrylic acid simultaneously with epihalohydrin and trimethylamine in an inert, polar solvent. The products of this reaction are separated by precipitation through the addition of a non-solvent, crystallization through a cooling procedure, or by selective extraction. The drawback of this process is the low yield; less than 83% based on trimethylamine and even lower based on the epihalohydrin and carboxylic acid. A major by-product, 3-chloro-2-hydroxypropyltrimethylammonium chloride, which comprises more that 25% of the reaction product has been identified in duplications of the patent examples.
Polish Patent 119,898 relates to a process for making MAHTAC by reacting methylmethacrylate with 3-chloro-2-hydroxyproplytrimethylammonium chloride (CHPTAC) in dimethylsulfoxide. The process involves distillation and separation. One drawback of this process is that the solubility of CHPTAC in the reaction medium is low, which leads to low reaction rates unless the other reactant is present in very high concentrations.
British Patent 1,112,912 and Belgian Patent 688,940 teach a method of producing MAHTAC by reacting potassium methacrylate with 3-chloro-2-hydroxypropyltrimethylammonium chloride in solvents such as acetonitrile or ethanol. In their Example 1, the reaction is carried out in acetonitrile. Potassium chloride is reported to precipitate from the reaction medium and is filtered. Tan colored MAHTAC with a broad melting range of 173.degree.-180.degree. C. is isolated by distilling off the acetonitrile. The MAHTAC then had to be recrystallized from a mixture of isopropanol and ethyl acetate. We have attempted to duplicate the results of this Example without success. Since the concentrations of potassium methacrylate and CHPTAC are not specifically defined in the case, we carried out reaction at three different concentrations The first one assumed that 1 part was one gram, the second 0.5 grams and the third 0.2 grams. In all cases the reaction was heterogeneous. Potassium methacrylate (PMA) and CHPTAC are only sparingly soluble in acetonitrile. This limits their concentrations in the reaction medium and keeps the reaction rate low. The products also have low solubility. The solubilities, in decreasing order are: PMA&gt;MAHTAC&gt;CHPTAC&gt;KCl. At no point was it possible to separate KCl leaving behind a MAHTAC solution. It was not possible to simply separate MAHTAC uncontaminated by the other salts. MAHTAC yields were measured to be less than 51.1% and even after recrystallization from 1:1 isopropanol and ethyl acetate the purity was only 58.2%. The reaction conditions are presented in Example 7. It is possible that the experiments in these patents may have been contaminated with water or another agent which yielded an unverifiable result.
None of the above processes produce a high purity product in high yield. It is desirable to have a process which does both economically.
Accordingly, it is an object of this invention to provide a process for the preparation of 3-(2-substituted acryloyloxy)-2-hydroxypropyltrialkylammonium chloride monomers and their isomers, and more particularly, 3-methacryloyloxy-2-hydroxypropyltrimethylammonium chloride monomer and its isomer wherein, for a given reaction time, the yield is higher than in current processes and the purity of the product is higher.
It is another object of this invention to provide a process wherein crystalline monomers having greater particle size and/or molecular weights can be obtained. Still other objects of this invention will be apparent to those skilled in the art upon reference to the following detailed description and the claims.